BASIC Tech Group - MyNews - 43 Next project, a QRP PA

The final box in my chain of QRP station items for digital transmissions is to be a 3.2W QRP PA. The block diagram for this is:



I have found a 3.2W RF amplifier module on eBay which I will use. It has a gain of 35dB and works from a +12V supply (I tried another one to play with and it worked well, but was only 2W). To drive this from my VFO I will use an external 20dB attenuator and adjust the output with the variable gain buffer of the VFO.

Next in the chain are a set of 3 switched LPFs for 40, 30 & 20m followed by a SWR bridge. All is controlled by an Arduino Nano microcomputer. This switches the LPF relays, reads the SWR bridge and displays FWD forward power and SWR on an OLED display. RX/TX switching is automatic when ever the PA forward output is above 100mW. So far I have developed some provisional software, you can see the OLED display, and a wired up an SWR detection board. Now to breadboard the AD8307s for detection of FWD & REF outputs from the bridge, and drive the Nano analog inputs for the display...



By the way in the background you can see my SDR-ELEKTOR, RF_POWER_METER and VFO running Hellschreiber S-MT software transmitting a HELL_S-MT beacon signal, displayed on the screen in Argo software: